An internal combustion engine inducts air to mix with fuel for combustion. Combusting the air and fuel raises pressure in engine cylinders which is translated into torque via engine pistons and a crankshaft. Exhaust gas exits the cylinders to make way for subsequent combustion events in the cylinder. The flow of exhaust gas from engine cylinders may be restricted by a catalyst or another device in the exhaust system such as a turbocharger turbine. At higher engine speeds and loads, pressure of exhaust gas in the exhaust manifold may be sufficiently high to cause closed exhaust valves to temporarily open. In particular, exhaust pressure acting on a back side of exhaust valves may be sufficient enough to overcome exhaust valve spring pressure, thereby opening one or more engine exhaust valves. An exhaust valve that opens in an untimely manner may reduce engine efficiency and degrade engine performance. Therefore, it may be desirable to provide a way of reducing the possibility of an exhaust valve opening when it is expected to be closed.
The inventors herein have recognized the above-mentioned issues and have developed a an engine operating method, comprising: locking an exhaust valve of a cylinder in a closed position via a mechanism other than a valve spring in response to the exhaust valve being in mechanical communication with a base circle of a camshaft lobe.
By locking an exhaust valve in a closed position while the exhaust valve is in communication with a base circle of a camshaft, it may be possible to prevent the exhaust valve from opening at times when exhaust valve opening may be undesirable. An exhaust valve is in mechanical communication with, or in direct or indirect contact with, the exhaust cam lobe base circle when the exhaust valve or a tappet in contact with the exhaust valve is contacting the exhaust cam lobe base circle, but the exhaust valve may not be in contact or mechanical communication with the exhaust cam base circle through the exhaust cam lobe itself. For example, during high engine load conditions, exhaust valves may be locked closed so that exhaust pressure from other engine cylinders may be prevented from opening closed exhaust valves so that cylinder charge may not be diluted with excess exhaust gas recirculation. The exhaust valve locking mechanism may be mechanically driven or it may be electromechanically driven. In one example, exhaust valves may be locked via inserting a pawl into a groove in a stem of an exhaust valve. The pawl holds the exhaust valve closed in the presence of higher exhaust pressures.
The present description may provide several advantages. Specifically, the approach may reduce the possibility of untimely exhaust valve openings. Further, the approach may be accomplished via mechanical or electromechanical mechanisms. Additionally, diagnostics may be made part of the approach so that mitigating actions may be taken if the exhaust valve locking mechanism degrades.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.